Because of characteristics of self-illumination, fast response, wide viewing angle, capability of being manufactured on a flexible substrate and the like, organic light emitting diodes (OLEDs) have been applied in the high-performance display field more and more. An OLED comprises a cathode, an anode and a functional layer located between the cathode and the anode. For example, the functional layer comprises an organic light emitting layer and may further comprise a hole injection layer, a hole transport layer, an electron transport layer and an electron injection layer. For the organic light emitting layer, there have been proposed many kinds of film forming methods, comprising an evaporation film forming method, a molecular beam epitaxy method, an organic chemical vapor deposition method, a sol-gel method and the like. The evaporation film forming method has advantages that operation is easy, a film thickness can be easily controlled, pollution to a thin film is small, doping can be achieved easily, and so on, and therefore the evaporation film firming method is generally adopted to form the organic light emitting layer and other organic functional film layers. A process for forming the organic functional layer by using the evaporation film forming method is conducted as follows: in a vacuum environment, an organic material is heated to allow it to be evaporated (sublimed) and then deposited on a target substrate to form a corresponding film layer.
In an evaporation process, the substance evaporated out of the evaporation source is diffused and deposited towards the target substrate in a generally conical radial shape, a problem that the film layer formed on the substrate is not uniform in thickness is caused easily, resulting in that a brightness or color shift occurs to a display panel, and therefore product quality is degraded.